1. Field of the Invention
The present invention relates to a contact charger, and more specifically relates to a contact charger and image forming apparatus provided with same for use in image forming apparatus of copying machines, facsimiles and the like.
2. Description of the Related Art
In image forming apparatus such as electrophotographic copying machine, printers, facsimiles and the like, the surface of an electrostatic latent image carrying member such as a photosensitive drum or the like is charged by means of a charging device. The charged surface of the electrostatic latent image carrying member is subjected to image light exposure to form an electrostatic latent image thereon. The thus formed electrostatic latent image is subsequently developed so as to be rendered visible, transferred onto a transfer medium, and fixed on said transfer medium.
Various types of such charging devices are known. Examples of such charging devices include corona chargers which utilize a corona discharge via a corotron system, scorotron system, serrated electrode array system or the like, and contact chargers wherein a charging member such as a brush, roller, film, belt or the like is brought into contact with the surface of the electrostatic latent image carrying member.
Chargers that utilize a corona discharge are advantageous insofar as they provide stabilized charging, however they also have certain disadvantages in that they produce large amounts of ozone, which leads to deterioration of the electrostatic latent image carrying member, and adversely affects humans. Thus, attention has become focused on contact chargers which produce markedly less ozone compared to corona chargers.
However, contact chargers using a film as a charging member are disadvantageous insofar as labor and time are necessarily involved in manufacturing a brush. Contact chargers that use a roller as a charging member have complex constructions due to the necessity of providing a mechanism to drive the roller. Since the charging roller is in direct contact with the electrostatic latent image carrying member even when the image forming apparatus is not operating, some deformation of said electrostatic latent image carrying member occurs due to the weight of said charging roller, such that said deformation causes inadequate charging of the electrostatic latent image carrying member. Contact chargers that use a plate as a charging member are susceptible to soiling of the electrostatic latent image carrying member, e.g., due to adhesion of developer and the like on the latent image carrier, and such soiling causes irregular charging of the electrostatic latent image carrying member, thereby producing nonuniform images and the like. Contact chargers that use a belt-like charging member increase the-size of the apparatus, and have the further disadvantage of having complex constructions due to the necessity of providing a mechanism to drive the belt.
U.S. patent application No. 5,192,974 discloses a contact charger of a film type for charging the surface of an electrostatic latent image carrying member via contact of said surface of an electrostatic latent image carrying member by a film supported by an end portion. However, in the aforesaid film-type contact charger, the film becomes soiled with developer and the like while image formation continues, such that streak-like charging irregularities are produced on the electrostatic latent image carrying member, which cause areas of dot-like high electric potential on the surface of the electrostatic latent image carrying member under environmental conditions of low temperature and low humidity.